The invention relates generally to medical assessment devices and more particularly to a system and a method for assessing the functional status of a subject.
Functional status forms an important component in the assessment of a patient""s clinical course. The abilities to stand, walk a prescribed distance, or perform routine daily tasks are examples of activities that provide general classification levels for functional status. Gathering information related to functional status of a patient generally requires the judgment of a clinical observer or requires the use of a validated self-assessment questionnaire. Patient difficulties in maintaining balance are intimately tied to their functional status. For patients who are very unsteady, the act of standing is sometimes a major accomplishment. The patient may wobble significantly and visibly as he/she goes through the process of standing. Patients having better balance control wobble less and enjoy higher levels of activity, and consequently, they have a higher functional status. Thus, a patient""s wobbling is a cue for a low level of functional status.
There are number of prior art systems that are useful in testing the ability of a patient to control his/her balance. U.S. Pat. No. 5,627,327 to De Luca et al. describes a system and a method for analyzing the postural control ability of a patient. The system of De Luca et al. includes a force platform, which is connected to a processor. The force platform is used to derive the center of pressure when a patient stands on the platform. The system generates a stabilogram diffusion plot by computing the mean square displacement of the center of pressure over time. The system can then calculate a Brownian diffusion coefficient, which is indicative of the level of stochastic activity of the center of pressure, from the slope of the stabilogram diffusion plot.
U.S. Pat. No. 5,627,327 to Zanakis describes a system for determining the physical instability of a patient. The system of Zanakis includes a stable platform that generates signals, which depend on the magnitude and direction of the force applied to the face of the platform. The system also includes a convex rocker dish with a flat surface on which a patient stands. The curved side of the rocker dish is placed on the platform. Thus, the convex rocker dish is an unsteady structure. The platform is connected to a display screen via a computer. The signals from the platform are used to generate a cursor on the screen. The position of the cursor is made to vary, depending the orientation of the flat surface on the rocker dish with respect to the face of the platform. Therefore, a patient standing on the rocker dish is able to manipulate the cursor on the screen by changing the orientation of the rocker dish. The physical instability of the patient is determined by measuring the time required for the patient to move the cursor to a target area on the screen by manipulating the rocker dish.
Although these known systems operate well for their intended purpose, what is needed are a system and a method for objectively assessing the functional status of a patient.
A system and a method of objectively assessing the functional status of a subject utilize a functional status scale to extract objective measures that are indicative of the subject""s functional status. The objective measures are extracted from center-of-weight (C.O.W.) data gathered from the functional status scale when the subject is standing on the scale. These objective measures can then be used to assess the current functional status of the subject by a health care provider. The functional status scale can be remotely stationed at the subject""s home, which eliminates the need for office visits, expensive home nurse visits, telephone interviews or video visits to assess the current functional status of the subject.
The system includes a communications hub that allows the functional status scale to be connected to a traditional wired telephone communications provider or to a cellular phone communications provider via a wireless connection when a direct wire connection is not possible. The system also includes a health care provider""s patient database, which is connected to the traditional telephone communications provider and the cellular phone communications provider. Thus, information from the functional status scale can be transmitted to the patient database through either a wireless connection via the communications hub or a direct wire connection via the traditional telephone communications provider. The patient database may be embodied in a computer, which allows a health care provider to directly access the stored information in the database. The patient database can be linked to the Internet or other network, such as a LAN or WAN, so that the stored information in the database can be accessed by remote computer through one of these established communications infrastructures.
The functional status scale includes weight sensors that are connected to a C.O.W. computer. Each of these weight sensors is designed to generate a weight signal that is proportional to the amount of vertical (downward) force on the weight sensor, when a subject stands on the scale. The C.O.W. computer is configured to generate signals that represent x and y coordinates of C.O.W. by processing the weight signals from the weight sensors. The C.O.W. computer is also configured to generate a signal that represents the weight of the subject.
The functional status scale also includes a processor, a storage device, a display and a communications interface module. The processor is connected to the C.O.W. computer to receive the signals computed by the C.O.W. computer. The signals that represent the C.O.W. can then be stored in the storage device or relayed to the communications interface module for transmission to the health care provider""s patient database. The communications interface module includes a modem and a radio frequency (RF) transceiver. The modem is used to establish a wire connection with the traditional telephone communications provider, while the RF transceiver is used to establish a wireless connection with the communications hub. The signal that represents the weight of the subject can be processed by the processor to drive the display of the functional status scale to alphanumerically present the weight of the subject. Thus, the functional status scale can operate as a conventional weight scale.
The computers of the system that are used to access the health care provider""s patient database include statistical and frequency domain analysis modules that are configured to extract the objective measures from the C.O.W. data transmitted from the functional status scale. These modules can be implemented as software and/or hardware. The statistical analysis module is configured to extract statistical measures that can be utilized for assessment of a subject""s functional status. Examples of statistical measures that may be extracted by the statistical analysis module include maximum x and y coordinate values, autocovariance of x and y, autocovariance of time (response time), standard deviation of x and y, mean magnitude excursions for x and y, maximum rate of change for x and y, statistical run length with short and long emphasis, cross correlation coefficient between x and y, cross-covariance between x and y, and cross-covariance length. The frequency domain analysis module is configured to extract frequency domain measures that can be utilized for functional status assessment. Examples of frequency domain measures that may be extracted by the frequency domain analysis module include dominant frequency for x and y coordinates, phase for the dominant frequency, mean power bandwidth, amplitude rank (largest to smallest) of frequency components, phase rank (largest to smallest) of frequency components, means square phase, mean phase, mean frequency, rms frequency, and rms phase.
The computers of the system may include other analysis modules that utilize different analytical approaches, such as chaos and fractal analyses, to extract additional measures for assessment of a subject""s functional status. In an alternative configuration, the analysis modules may be included in the functional status scale, rather than the remote computers. In this alterative configuration, the measures computed by the analysis modules are transmitted from the functional status scale to the health care provider""s patient database, instead of the signals that represent x and y coordinates of the C.O.W.
In a first embodiment, the functional status scale includes four weight sensors that are positioned in a rectangular configuration. In a second embodiment, the functional status scale includes four weight sensors that are positioned in a diamond-like configuration. In a third embodiment, the functional status scale includes three weight sensors that are positioned in a triangular configuration. In each of these embodiments, the C.O.W. computer is configured accordingly to compute the x and y coordinate signals from the weight signals generated by the three or four weight sensors.
The method of objectively assessing the functional status of a subject in accordance with the invention includes a step during which weight signals are generated by weight sensors of a functional status scale in response to the subject""s weight when the subject is standing on the scale. Using these weight signals, x and y coordinates of the center-of-weight are computed by a C.O.W. computer of the functional status scale. Next, a communications link is established between the functional status scale and a health care provider""s patient database. The x and y coordinates are then transmitted to the health care provider""s patient. Next, the x and y coordinates are analyzed by one or more analysis modules included in a remote computer that has communicated with the health care provider""s patient database. During this step, functional status measures are extracted from the x and y coordinates by the analysis modules. The functional status measures may be derived by statistical analysis, frequency domain analysis or other analytical approaches. These functional status measures provide objective criteria for assessment of the current functional status of the subject.